Which mechanism most directly enabled early submarines, such as *Turtle* (1776), to submerge and surface effectively?

💡 Explanation

When the submarine needs to submerge, ballast tanks are flooded, increasing the vessel's density and causing it to sink; venting the tanks with compressed air decreases density for surfacing. Therefore ballast tank flooding and venting results, rather than hydraulic fins, engines, or electromagnetic propulsion which were later innovations.

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